In recent years, necessity has been increased for developing technology to adjust and control the hydrophilic or hydrophobic properties of the surface of a material, for accommodating them to applications and objects. For example, such a technology is required in a field of a cell array as one of bio-chip technique. In the field, matrix-like microregions are arranged on a glass substrate for cultivating cells and screening a chemical solution therein. In this treatment, in order to accomplish a lot of screenings in a smaller space, it is necessary to form these micro-media as an array in a pattern having hydrophilic portions and hydrophobic portions for being independent microregions on the surface of the substrate. Further, the bio-chip is progressively applied to genome analysis, food inspection, and tailor-made medicines, and thus controlling the superficial wettability applicable to various things is demanded, but not limited to those for the fixing of a cell solution. Moreover, studies of micro-TAS, micro-reactors, lab-on-a-chips, and the like have been progressed, and accordingly technology is demanded for controlling the fluidities of various kinds of liquid to satisfy the requirement in miniaturization of devices for the above-described purpose.
In order to impart hydrophilic or hydrophobic properties to the surface of a substrate or the like, methods of coating a hydrophilic or hydrophobic agent have been adopted so far. However, in these methods, the property of the surface cannot be changed dynamically (retroactively and reversibly). The property depends basically on the coating agent, and therefore it is limited to either of hydrophilic and hydrophobic properties.
To solve the above described problems, a trial is made to control the superficial wettability of a substrate or the like, more functionally. For example, it is proposed to change the superficial wettability by applying light or electrons to the surface (see Patent Documents 1 to 3). Further, it is proposed that a method controls the wettability by oscillation (see Patent Document 4).
Besides, Non Patent Document 1 discloses a method of applying voltage to a liquid to change the surface tension thereof. However, in this method, it is necessary to apply voltage to the liquid continuously for maintaining wettability, and the output should be varied depending on the kind of liquid and the dissolved material. Further, in the case that plural liquids are handled in a single device, contaminations are concerned due to excess liquids passing through the same passage, and therefore such a method can not be adopted. Moreover, Non Patent Document 2 discloses a method of using a polymer which can be deformed by heating to change its wettability.    [Patent Document 1] JP-A-11-90217 (“JP-A” means unexamined published Japanese patent application)    [Patent Document 2] JP-A-2003-155357    [Patent Document 3] JP-A-2000-119551    [Patent Document 4] JP-A-2001-347218    [Non Patent Document 1] Journal of Microelectromechanical System, Vol. 12, No. 1, 2003    [Non Patent Document 2] Searched on Apr. 8, 2005, (Heisei 17), Internet <URL:http://www.cellseed.com/technology.html>